Powers:Jahf is immensely strong (Class 100) and virtually indestructible. He is, however, susceptible to certain sonic attacks, which can incapacitate him.

He is programmed to not allow anyone to approach the Crystal during the once-every-million-years event when the Death-stars are in alignment. During the time in-between these alignments, Jahf still serves to protect the Crystal from harm. If Jahf is defeated, the immense Modt--who is 1000x more powerful than Jahf--appears to stop any intruder; if Modt is defeated, an as-yet unidentified being, allegedly 1000x more powerful that Modt, would appear to stop any intruder; this succession would reportedly continue until any potential invader is defeated. The Crystal has allegedly granted Jahf and Modt leave to act on its behalf.

He is unique to the multiverse. While Jahf is highly powered to guard the Crystal, he cannot directly affect it in any way. According to one account, he is a living facet of the crystal itself, empowered by the entire neutron galaxy at its heart--completely invulnerable, indestructible, and invincible.

When the M'Kraan Crystal's nine Deathstars came into alignment and the M'Kraan Crystal opened up to the outside world, Jahf appeared to prevent anyone from entering it. Wolverine laughed at his threats, and Jahf punched him into orbit. Jahf shrugged off the combined assaults of the X-Men and Starjammers. Phoenix summoned a meteor from orbit and crashed it into Jahf, who was completely unharmed. Taking note of Jahf mentioning his programming, Banshee surmised that he was a robot and he used his sonic powers to "scramble his circuits." Jahf grabbed Banshee and nearly crushed him to death, but Banshee managed to blast him in time, and Jahf collapsed, inert.

As similar events occurred in the alternate reality of Earth-913, Jahf was apparently defeated by the Starjammers or the Shi'ar Imperial Guard, as Modt was seen to be battling the Imperial Guard when the X-Men arrived.

Jahf was present--though unable to do anything about it--when Phoenix (Rachel Summers) transported the X-Men into the M'Kraan Crystal in an abortive attempt to destroy the universe in order to stop the Beyonder.

Following Legion's journey into the past in an effort to kill Magneto, Jahf appeared on Chandilar, easily overpowering the mighty Gladiator and confronting Lilandra. He told her that the End of All That Is was approaching and that he may soon no longer guard the M'Kraan Crystal.
Bishop, Iceman, Psylocke, and Storm managed to latch onto Legion's energies and follow him into the past.

In trying to kill Magneto, Legion accidentally killed Xavier. This created a new reality, Earth-295, the Age of Apocalypse, in which Apocalypse gained ascendance without Xavier or his followers to slow his path.
The Earth-616 reality was washed over completely by the crystallization wave.

In the Earth-295 reality, Deathbird, Lila Cheney, and Gambit entered the M'Kraan Crystal, where they encountered Jahf who led them to the Sphere. Both Lila and D'Ken were held transfixed by red light emitted by the Sphere, and as Deathbird attempted to kill D'Ken, she was transfixed as well. Jahf told Gambit how the damage to the Earth-616 reality would soon cause realities around it to collapse, one after the other: The End of All There Is. Jahf told him that by taking a shard of the Crystal and using it to send Bishop back in time to stop Legion from killing Xavier, he could save reality. Jahf further told him that in order to take a part of the Crystal, Gambit would have to leave a part of himself.
As the World was awash with crystallization waves, the other X-Ternals entered the Crystal as well to escape its effects, and Gambit offered his love of Rogue to the Crystal. He struck the Sphere, which granted him a shard of the Crystal while at the same time elatedly singing a song of freedom as it liberated itself from D'Ken's fusion-energy absorption system.

On Earth-295, via the M'Kraan shard Destiny located Earth-616, Illyana opened a portal into it, and Bishop stopped Legion from killing Xavier, reversing the damage done to Earth-616 and ending the threat from the M'Kraan Crystal. The Sugar Man, Dark Beast, Nate Grey, and Holocaust were also transported to Earth-616 via the M'Kraan Crystal.

A hologram of Jahf appeared in Lilandra's bedchambers, informing her of energy being drained from the M'Kraan Crystal to Earth. He described this as blasphemous to their faith, and he was satisfied when she took steps to put a stop to this. The sources of the energy drains proved to be the four natives of Earth-295 dwelling on Earth-616, and the connections to the M'Kraan Crystal were severed.

Modt and Jahf sensed unsettling vibrations in the M'Kraan Crystal caused by a portal that opened to Earth-295, through which some Infinites had passed. Nate Grey, with the help of Cyclops and Phoenix (Jean Grey) closed the portal.

Modt and Jahf--with the Crystal's leave--traveled to Earth-616 to investigate the sole remaining trace of Earth-295 energy: Nate Grey. To test his abilities they disguised themselves as a father and son injured by a falling tree, and the father (Modt) tried to convince Nate to use his powers to heal "Jeff" (Jahf). Nate refused to tamper with reality, but when he was able to see through their illusions, Jahf decided that he was too dangerous to live. Cyclops, Phoenix, and Nate battled the powerful M'Kraan guardians, but ultimately Modt agreed that while Nate's power was a danger, he had demonstrated good judgment and self-control, and that he did not have to be destroyed. Modt forcibly restrained Jahf and took him back to the M'Kraan Crystal.

Gladiator met with Jahf, convinces him to allow them to the hold the wedding of Deathbird & Vulcan under the M'kraan Crystal under the assurance that none would touch it.

D'ken and Araki planned the royal wedding of Deathbird & Vulcan, intending to cast Xavier into the Crystal during the ceremony.
As D'ken completed the ceremony, the Starjammers, X-Men, and Shi'ar rebel forces arrived. During the ensuing battle Vulcan cast Xavier into the M'kraan Crystal, and Darwin followed, hoping to save Xavier. Darwin found Xavier within the Crystal and escaped with him. The exposure to the M'kraan Crystal restored Xavier's mutant powers, perhaps stronger than ever before.